Structures including layers of polyimide are known. Polyimide is a material which due to its dielectric properties and its chemical and mechanical resistance is attractive for many applications. It is also known to adapt the properties of polyimide for special purposes by blending a filler into the polyimide.
In the article "Screenable Alpha Particle Barrier", published in the IBM Technical Disclosure Bulletin, Vol. 23, No. 12, May 1981, p. 5281 is described that a solution containing a polyamic acid and boron nitride particles is screened on substrates to form an alpha particle barrier. The boron nitride particles, which are in the form of platelets also act as a thermally conducting material to increase heat transfer.
The article "Screened Multilayer Polyimide", published in the IBM Technical Disclosure Bulletin, Vol. 23, No. 1, June 1980, p. 109, teaches the formulation and use of a screenable adherent polyimide paste with low flow characteristics. In this paste graphite is used as a filler acting as a sponge to absorb the solvents in which the polyamic acid is dissolved. Thus, the graphite prevents excessive bleedout of the polyimide precursors and undesired flow. In use the paste is screened on a clean dry substrate and then cured at 350.degree. C. Such a graphite-filled polyimide can be used to form a resistitive layer or capacitive layer. If desired, such formed resistive layers can have metallization either evaporated or sputtered thereon.
EP-A- No. 00 30 641 describes a blanket or selective coating consisting of polyimide and mica platelets. To produce the coating a solution of a polyamic acid containing the mica platelets is applied to a substrate either uniformly or through a screen having a desired pattern. The solvent is removed and the resulting layer is cured to a solid adhering coating. The coating is preferably used to insulate current-carrying metal patterns exposed on ceramic substrates onto which silicon chips with integrated circuits are mounted.
U.S. Pat. No. 3 615 913 describes polyimide and polyamide-polyimide coatings used as passivators for semiconductor surfaces and the production of such coatings. The coating contains a filler which consists of an electrically insulating material selected from the group of aluminum oxide, silicon oxide, glass fibers, boron nitride, quartz, mica, magnesium oxide and reactivated polytetrafluorethylene.
U.S. Pat. No. 4 246 147 describes the composition, the application by screening, the usage and the stripping of a solder mask. The screenable and strippable solder mask composition contains a polyepoxide or polyimide/amide, a detackifier, a high temperature resistant filler and a solvent. The applied solder mask protects predetermined areas on a substrate from the solder deposition. It is essential for the solder mask that it is readily strippable after its use. The solid filler must be one which is resistant to exposure to elevated temperatures. Examples of some suitable solid temperature resistant fillers include i.a. zinc oxide and alumina.